High data rate, point-to-point radio systems are used for a number of applications including enterprise network connectivity and telecommunications backhaul, first mile, and last mile connections. In general, the higher amount of Radio Frequency (RF) bandwidth that is allocated to the radio system, the higher the amount of data throughput that can be accommodated. In addition, the higher the underlying frequency of the RF carrier, the more directed the communications beam can be for a given size of antenna. Therefore, millimeter wave RF frequencies (from 30 GHz to 300 GHz) are used for point-to-point communications links in spite of higher rain attenuation than is suffered by lower frequencies because they have higher available allocated bandwidths (supporting high data rates), and because more radio links can be placed in a given area because of the narrower beams.
In addition to a Federal Communications Commission (FCC) regionally licensed millimeter wave band between 38.6 GHz and 40 GHz used for communications, there is a large unlicensed band from 57 GHz-64 GHz, and licensed bands extending from 71-76 GHz, 81-86 GHz and 92-95 GHz. A subsidiary of Applicants' assignee manufactures and sells FCC licensed and certified radio links in the 71-76 GHz and 81-86 GHz millimeter wave bands operating at data rates of 1.25 Gbps and higher. Applicants' assignee has a number of patents issued and pending covering various aspects of these radios and their applications. Some of these patents and pending patent applications include the following, all of which are incorporated herein by reference:
Pat. No.IssuedTitle6,556,836Apr. 29, 2003Point-to-Point Millimeter Wave Dual Band Free SpaceGigabit per Second Communication Link6,587,699Jul. 01, 2003Narrow Beamwidth Communication Link with AlignmentCamera6,611,696Aug. 26, 2003Method and Apparatus for Aligning the Antennas of aMillimeter Wave Communication Link using a NarrowBand Oscillator and a Power Detector6,665,546Dec. 16, 2003High Speed Point-to-Point Millimeter Wave DataCommunication System6,714,800Mar. 30, 2004Cellular Telephone System with Free Space MillimeterWave Trunk Line7,062,293Jun. 13, 2006Cellular Telephone System with Free Space MillimeterWave Trunk Line7,065,326Jun. 20, 2006Millimeter Wave Communication System with a HighPerformance Modulator CircuitPatent ApplicationsSer. No.FiledTitle11/212,322Aug. 25, 2005Millimeter Wave Communication with Grid Amplifier11/249,787Oct. 12, 2005Mobile Millimeter Wave Communication Link11/327,816Jan. 06, 2006Wireless System with Free Space Millimeter Wave TrunkLine11/452,631Jun. 13, 2006Wireless Millimeter Wave Communication System withMobile Base Station12/004,578Dec. 24, 2007Wireless Communication System w/ Lens-BasedTransceiver12/911,797Jan. 29, 2008Cellular Systems with Distributed Antennas12/080,709Apr. 03, 2008Cellular Communication System with High Speed ContentDistribution
To achieve higher data rates (such as OC-48 operating at 2.488 Gigabits per Second (Gbps)), applicant previously developed a radio using Quaternary Phase Shift Keying (QPSK) and a radio architecture using Up-converters and Down-converters, as described in FIG. 2, and previously disclosed in a patent application Ser. No. 11/452,631 which has been incorporated herein by reference. Applicant believes that other companies have also tried to develop radios with a similar architecture, but they are not aware of any radios operating at data rates as high as 2.488 Gbps which are being sold by other companies. Applicant believes that part of the reason for this might be that the cost of building a high data rate radio with this architecture is high. In the embodiment shown in FIG. 2, the transceiver transmits radiation centered at the 73.5 GHz millimeter wave frequency, and receives radiation centered at the 83.5 GHz millimeter wave frequency. A paired transceiver which communicates with the transceiver shown receives at 73.5 GHz and transmits at 83.5 GHz. All of the transceiver modules are identical for the two paired transceivers, except that the local oscillator and mixer module frequencies are reversed. This transceiver is compatible with phase shift keyed modulation, and amplifiers and high power amplifiers which can operate near saturation.
Digital data at a data rate of 2.488 Gbps (corresponding to fiber optic communications standard OC-48) is incident through a fiber optic cable as indicated at 401 to the Demark (Demarcation) box 400 on the left. Power is also supplied to this box, either at 48 V DC, or 110 or 220 V AC. This power is first converted to 48 V DC, and then the power is converted to low voltage DC power of various values such as +/−5V and +/−12 V by DC to DC power supplies for use by the various modules in the transceiver. The incoming 2.488 Gbps data then enters the Encoder module 402 where it is encoded in a format appropriate for QPSK modulation. If no error correction or auxiliary channel bits are desired, the incoming data is demultiplexed (on alternate bits) into two data streams at 1.244 Gbps. If error correction, encryption, or the addition of auxiliary channel bits are desired, these are added at this point resulting in two data streams at a slightly higher data rate. Bits from each data stream are then combined to form a dibit, and subsequent dibits are compared (essentially through a 2 bit subtraction process) to from an I and Q data stream which differentially encodes the incoming data. The I and Q data streams (at 1.244 Gbps if extra bits have not been added) drive a 4 phase modulator 404 which changes the phase of a 13.312 GHz oscillator signal. The output of the 4 phase modulator is a signal at 13.312 GHz as indicated at 404 which has its phase changed through 4 different possible phase values separated by 90 degrees at a baud rate of 1.244 Gbps. The amount of rotation from the previous state depends on the incoming digital dibit. (A 00 corresponds to no phase change, 01 to 90 degree phase change, 10 to 180 degree phase change and 11 to 270 degree phase change). The 13.312 GHz modulated oscillator signal is then combined with a 60.188 GHz local oscillator signal in mixer 406 to form a signal centered at 73.5 GHz. As indicated at 408 the local oscillator utilizes a phase locked dielectric resonant oscillator (PLDRO) signal at 10.031 GHz which has been multiplied in frequency by a factor of 6. The 73.5 GHz signal is then amplified to a power near 20 dBm (100 mw) by a first amplifier module 410, and then (optionally) amplified to a power near 2 W by a power amplifier 412. The amplified signal enters a frequency division diplexer 414 which routes the 73.5 GHz frequency band to an output waveguide, past a power detector 416 (to measure the transmit power) and then to a parabolic 2 foot diameter antenna 418 for transmission along a line of sight through free space to the paired transceiver.
At the same time, incoming millimeter wave radiation centered at 83.5 GHz transmitted by a paired transceiver (not shown) is received at the two foot parabolic antenna 418 and passes through the waveguide to the frequency division diplexer. The 83.5 GHz radiation is passed by the diplexer to the lower arm of the diagram in FIG. 2. It is then amplified by low noise amplifer 419 and mixed in mixer 422 with the signal from a local oscillator 420 operating at 10.188 GHz. The 71.188 GHz frequency is generate by multiplying a signal from a phase locked dielectric resonant oscillator (PLDRO) locked to a frequency of 11.698 GHz by a factor of 6 (through a times 2 and a times 3 multiplier). The output of mixer 422 is a signal centered at 13.312 GHz which is filtered and amplified by the IF Amplifier module 424. The receive signal strength is also measured at this stage. After further amplification and filtering, the incoming 13.312 GHz signal enters the demodulation and phase locked loop module 426 where the I and Q digital data streams are extracted. The I and Q data streams at 1.244 Gbaud then enter the decoder module where the 2.488 Gbps data stream sent from the paired transceiver is reconstructed. Decoder 402 basically computes the difference between sequential pairs of I and Q data, which corresponds to the dibits originally encoded at the paired transceiver. (The I and Q are related to the phase of the incoming signal with some ambiguity, but the difference in phase is known. If the phase has changed by 0 degrees, then the transmitted dibit was 00, 90 degrees corresponds to 01, 180 degrees corresponds to 10 and 270 degrees corresponds to 11). The decoded dibits are then remultiplexed into a 2.488 Gbps data stream for transmission to the demark box 400 and then through fiber optic cable 401 to the user.
The radio systems described above include state of the art systems and work well but are complicated and somewhat costly to fabricate. What is needed is a less complicated very high data rate millimeter wave radio system.